In recent years, many aircraft manufacturers have sought improved ice protection systems to enable aircraft to safely fly in atmospheric icing conditions. Ice accumulations on the leading edge surfaces of various aircraft structures can seriously effect the aerodynamic characteristics of an aircraft. Conventional pneumatic deicers, electrothermal deicers and bleed air anti-icers have been used for many years on general aviation or commercial aircraft. These ice protection techniques are described in detail by Technical Report ADS-4, Engineering Summary of Airframe Icing Technical Data published by the Federal Aviation Agency, December 1963. In spite of these proven techniques, many companies have expressed a desire for new systems having better ice removal performance, better life and reliability, and decreased weight and energy requirements.
In response to this need, a class of systems has been developed that utilize a force displacement generation means to dynamically activate a thin deflectable primary layer upon which ice accumulates. The dynamic activation induces rapid motion in the thin deflectable skin sufficient to dynamically debond, shatter and expel an accumulated ice cap into surrounding airflow. As will be discussed more fully, the force displacement generation means can take a variety of forms.
In some devices, the force displacement generation means are combined with the thin deflectable primary layer to form a unitary deicer. The unitary deicer is generally formed in a thin sheet that can be subsequently bonded to the exterior surface of an existing aircraft structure. The deicer is usually designed to be removed from the aircraft structure and replaced in the field requiring the use of a replaceable adhesive such as 3M 1300L rubber cement. Examples are presented in U.S. Pat. No. 4,706,911 METHOD AND APPARATUS FOR DEICING A LEADING EDGE, Briscoe et al. (hereinafter referred to as the Pneumatic Impulse Patent), U.S. Pat. No. 4,875,644 ELECTRO-REPULSIVE SEPARATION SYSTEM FOR DEICING, Adams et al. (hereinafter referred to as the Electro-Repulsive Patent), and U.S. Pat. No. 5,129,598 ATTACHABLE ELECTRO-IMPULSE Deicer, Adams et al. (hereinafter referred to as the Electro-Impulse Patent).
In other devices, the force displacement generation means are combined with the thin deflectable primary layer and a substructure thereby forming a unitary leading edge with integral deicing capability. This unitary leading edge structure replaces the entire leading edge of an aircraft structure such as a wing, engine inlet, horizontal stabilizer, or vertical stabilizer. An example of this type of device is presented in U.S. Pat. No. 5,098,037 STRUCTURAL AIRFOIL HAVING INTEGRAL EXPULSIVE SYSTEM, Leffel et al. (hereinafter referred to as the Integrated Pneumatic Impulse Patent).
In the Electro-Repulsive Patent, the force displacement generation means comprises an upper array of conductors and a lower array of conductors. The upper conductors are substantially parallel to each other and to adjacent conductors in the lower layer. The upper conductors are connected in series with the lower conductors so that a single continuous conductor is formed that passes from the upper layer, around the lower layer, back around the upper layer, and so on. Upon application of an electrical potential to the input leads, current is developed in the upper conductors that is in the same direction in all upper conductors. Likewise, current is developed in the lower conductors that is in the same direction in all lower conductors, but opposite to the direction of the current in the upper conductors. As explained in the Electro-Repulsive Patent, maintaining a constant current direction in all the conductors of a layer greatly increases the separation force between the two layers.
After installation of the deicer on a structural member (such as a leading edge), the upper and lower conductors are sandwiched between the structural member and a surface ply. Upon application of a high magnitude short duration current pulse, opposing electromagnetic fields in the upper and lower layers forcefully repel each other. This motion induces a dynamic motion into the surface ply which dynamically removes accumulated ice. As described in the Electro-Repulsive Patent, a current pulse that rises to between 2300 and 3100 amperes within 100 microseconds generates effective ice removal. A circuit for generating such a pulse is described in the Electro-Repulsive Patent. The circuit includes a pulse forming network, but this is not absolutely necessary.
Another form for force displacement generation means utilizing electromagnetic apparatus is illustrated by the Electro-Impulse Patent. A planar coil comprising at least one coiled conductor is sandwiched between a surface ply and a conductive substructure (such as an aluminum leading edge). Planar coils are described in great detail in U.S. Pat. No. 5,152,480 PLANAR COIL CONSTRUCTION, Adams et al. (hereinafter referred to as the Planar Coil Patent). As described in the Electro-Impulse Patent, a high magnitude short duration current pulse is applied to the coil. The current in the coil induces a strong rapidly changing electromagnetic field. The electromagnetic field generates eddy currents in the conductive substructure which, in turn, generates an opposing electromagnetic field. The two electromagnetic fields repel each other causing a repelling force between the coil and the substructure. The coil induces dynamic motion into the surface ply thereby dynamically removing accumulated ice. Effective ice removal is generated by a peak current of about 3000 amperes rising in a period of 100 microseconds. An electrical circuit for generating such a pulse is disclosed. The circuit is very similar to the circuit disclosed in the Electro-Repulsive Patent.
In the previous example, the force displacement generation means is composed of a single unitary planar coil. As described in the Planar Coil Patent, the single unitary coil can be formed from two or more superposed spiral shaped coils that are interleaved with thin dielectric layers and bonded together. A slightly different variation is required if the substructure does not have sufficient electrical conductivity to effectively develop eddy currents. For example, a target would be required with a fiber reinforced plastic substructure, or a conductive substructure that is too thin to effectively develop eddy currents. The target is a sheet of conductive material such as copper or aluminum that is located adjacent the coil. The coil and target are forcefully repelled upon application of a high magnitude short duration current pulse to the coil due to opposing magnetic fields generated by current in the coil and by eddy currents in the target. This motion induces dynamic motion into the surface ply which dynamically removes accumulated ice. The target can be formed as a part of the substructure or can be formed as a part of the force displacement generation means. Also, as described in the Electro-Impulse Patent, either the target or the coil can be located immediately subjacent the primary layer. The target applies the motive force to the skin if it is located subjacent the skin. Conversely, the coil applies the motive force to the skin if it is located subjacent the skin.
The Planar Coil Patent also teaches an electro-repulsive variation similar to the Electro-Repulsive Patent. Two mirror image unitary planar coils are superposed relative to each other and electrically connected so that upon application of a high magnitude short duration current pulse to each coil, current direction is opposite in each coil. Opposing electromagnetic fields are generated in the coils which causes each coil to forcefully repel the other. This motion induces a mechanical impulse into the surface ply which removes accumulated ice. This approach differs from the Electro-Repulsive Patent which utilizes a single conductor to form the upper and lower conductors.
A type of force displacement generation means that utilizes pressurized gas is described in the Pneumatic Impulse Patent and the Integrated Pneumatic Impulse Patent. A plurality of pneumatic tubes extend in a spanwise direction subjacent a thin deflectable primary layer (the primary layer is analogous to the surface ply previously discussed). The tubes and skin are supported by a fiber reinforced plastic substructure which together form a leading edge structure with integral deicing capability. Special fittings are integrated into the tubes at various locations spaced along the span of each tube. A pneumatic impulse valve is attached to each fitting. A suitable valve is described in U.S. Pat. No. 4,878,647 PNEUMATIC IMPULSE VALVE AND SEPARATION SYSTEM, Putt et al. The valve contains a small volume (about 1 cubic inch) of high pressure air (500 to 5,000 psig). Upon activation by a solenoid, the valve quickly releases the pressurized air into each tube via the fitting. The expanding air pulse causes the tube to expand and induce mechanical motion into the skin thereby dynamically expelling accumulated ice. The expanding air pulse most preferably inflates the tube in less than 500 microseconds.
As evidenced by the previously described Electro-Repulsive, Electro-Impulse, Planar Coil, Pneumatic Impulse, and Integrated Pneumatic Impulse patents, many variations of force displacement generation means have been developed. The devices described above exhibit various advantages over older deicing systems relating to ice removal, weight, durability, life, and energy consumption. Improved force generation devices have, however, presented challenges in providing a platform capable of reliably withstanding the transferred force, because although effective ice shedding forces can be delivered, the deicer skin tends to fatigue and fail prematurely at unacceptable rates.
A deicer is therefore desired which exhibits excellent ice removal performance typical of the devices described above while having increased life and reliability.